1. Field of the Invention
The present invention relates to an automotive alternator, and in particular, relates to a construction for coil end groups of a stator winding of the automotive alternator enabling a stator to be cooled efficiently by reducing a flow rate of cooling air flowing through the inside of a rotor.
2. Description of the Related Art
FIG. 5 is a cross section showing a conventional stator for an automotive alternator.
The conventional automotive alternator is constructed by rotatably mounting a Lundell-type rotor 7 by means of a shaft 6 inside a case 3 constituted by an aluminum front bracket 1 and an aluminum rear bracket 2, and fastening a stator 8 to an inner wall of the case so as to cover an outer circumferential side of the rotor 7.
The shaft 6 is rotatably supported in the front bracket 1 and the rear bracket 2. A pulley 4 is fastened to a first end of this shaft 6 so that rotational torque from an engine can be transmitted to the shaft 6 by means of a belt (not shown).
Slip rings 9 for supplying electric current to the rotor 7 are fastened to a second end of the shaft 6, and a pair of brushes 10 are housed in a brush holder 11 which is disposed inside the case 3 such that the pair of brushes 10 slide in contact with the slip rings 9. A regulator 18 for adjusting the output voltage generated in the stator 8 is fastened by adhesive to a heat sink 17 fitted onto the brush holder 11. A rectifier 12 which is electrically connected to the stator 8 and converts alternating current generated in the stator 8 into direct current is mounted inside the case 3.
The rotor 7 is constituted by a rotor winding 13 for generating magnetic flux on passage of electric current, and a pair of pole cores 20 and 21 disposed so as to cover the rotor winding 13, magnetic poles being formed in the pole cores 20 and 21 by the magnetic flux generated in the rotor winding 13. The pair of pole cores 20 and 21 are made of iron, each has a number of claw-shaped magnetic poles 22 and 23 disposed on an outer circumferential perimeter at even pitch in a circumferential direction so as to project axially, and the pole cores 20 and 21 are fastened to the shaft 6 facing each other such that the claw-shaped magnetic poles 22 and 23 intermesh. In addition, fans 5 are fastened to first and second axial ends of the rotor 7.
The stator 8 is constituted by a stator core 15, and a stator winding 16 composed by winding a conducting wire into the stator core 15, an alternating current being generated in the stator winding 16 by changes in the magnetic flux from the rotor 7 accompanying rotation of the rotor 7.
In the automotive alternator constructed in this manner, electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor winding 13, generating magnetic flux. The claw-shaped magnetic poles 22 of the first pole core 20 are magnetized with north-seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 23 of the first pole core 21 are magnetized with south-seeking (S) poles. At the same time, rotational torque from the engine is transmitted through the belt and the pulley 4 to the shaft 6, rotating the rotor 7. Thus, a rotating magnetic field is applied to the stator winding 16, generating electromotive force in the stator winding 16. This alternating electromotive force passes through the rectifier 12 and is converted into direct current, the output is adjusted by the regulator 18, and the battery is recharged.
In the automotive alternator, the stator winding 16, the rectifier 12, the regulator 18, etc., constantly generate heat while generating electricity. Thus, in order to cool the heat generated by power generation, front-end and rear-end air intake openings 1a and 2a and front-end and rear-end air discharge openings 1b and 2b are disposed in the front bracket 1 and the rear bracket 2.
At the rear end, a cooling air flow QR is formed by the rotation of the fans 5, cooling the rectifier 12, the regulator 18, and a rear-end coil end group 16r of the stator winding 16. In other words, external air is drawn in by the rotation of the fans 5 through the rear-end air intake openings 2a disposed facing both a heat sink 19 on the rectifier 12 and the heat sink 17 of the regulator 18, cooling the rectifier 12 and the regulator 18, then passes through fan blades 5a from an inner radial side to an outer radial side, cooling the rear-end coil end group 16r of the stator winding 16, and is discharged to the outside through the rear-end air discharge openings 2b. 
At the same time, at the front end, a cooling air flow QF is formed by the rotation of the fans 5, cooling a front-end coil end group 16f of the stator winding 16. In other words, external air is drawn in by the rotation of the fans 5 through the front-end air intake openings 1a in an axial direction, then passes through the fan blades 5a from a radially inner side to a radially outer side, cooling the front-end coil end group 16f of the stator winding 16, and is discharged to the outside through the front-end air discharge openings 1b. 
In addition, a cooling air flow QRt flowing through the inside of the rotor 7 is generated as a result of a pressure difference between the front end and the rear end, cooling the rotor 7.
Now, because the stator winding 16 generates a high degree of heat, and output properties of the stator winding 16 deteriorate when the temperature is high, the stator winding 16 is constructed so as to enable reliable cooling by positioning the front-end and rear-end coil end groups 16f and 16r thereof between the fan blades 5a and the front-end and rear-end air discharge openings 1b and 2b, respectively.
Next, the stator winding construction used in the conventional automotive alternator will be explained with reference to FIG. 6. Moreover, FIG. 6 is a partial enlargement of the conventional stator viewed from an inner circumferential side.
In FIG. 6, the stator core 15 is formed into a cylindrical shape, and a number of slots 15a having a groove direction in an axial direction are disposed at even pitch in a circumferential direction so as to open onto the inner circumferential side. The stator winding 16 is constructed by joining together, using arc welding or the like, free end portions 29c of coil segments 29 inserted into pairs of slots 15a in which the slots 15a in each pair are three slots apart, so as to adopt a predetermined winding construction. As shown in FIG. 7, each of the coil segments 29 is a short segment of a conductor such as copper or the like having a circular cross section coated with insulation, the conductor being formed into a general U shape composed of a pair of straight portions 29a linked by a generally V-shaped turn portion 29b. 
At the front end of the stator core 15, front-end coil ends 24 formed into a connection pattern composed of pairs of front-end root portions 24a extending outwards from pairs of slots 15a three slots apart, pairs of front-end inclined portions 24b bent from each of the pairs of front-end root portions 24a and extending in a circumferential direction, and pairs of front-end joining portions 24c connecting together end portions of the pairs of front-end inclined portions 24b, are arranged in a circumferential direction to constitute the front-end coil end group 16f. Moreover, the front-end joining portions 24c correspond to joint portions joining together the free end portions 29c of the coil segments 29.
Similarly, at the rear end of the stator core 15, rear-end coil ends 25 formed into a connection pattern composed of pairs of rear-end root portions 25a extending outwards from pairs of slots 15a three slots apart, pairs of rear-end inclined portions 25b bent from each of the pairs of rear-end root portions 25a and extending in a circumferential direction, and pairs of rear-end joining portions 25c connecting together end portions of the pairs of rear-end inclined portions 25b, are arranged in a circumferential direction to constitute the rear-end coil end group 16r. Moreover, the rear-end coil ends 25 correspond to the turn portions 29b of the coil segments 29.
In the stator winding 16 constructed in this manner, inner circumferential surfaces of the coil end groups 16f and 16r face the fan blades 5a and constitute blade-facing surfaces. The inclined portions 24b and 25b of the coil ends 24 and 25 constituting the blade-facing surfaces, that is to say, the inclined portions 24b and 25b positioned on the inner circumferential sides of the coil ends 24 and 25, are inclined so as to be parallel to each other and to be at a predetermined angle relative to the axis of the stator core 15.
A manufacturing method for the conventional stator winding 16 will now be explained with reference to FIGS. 8 and 9.
First, as shown in FIG. 8, the coil segments 29 are inserted from the rear end into pairs of slots 15a three slots apart. At that time, each of the coil segments 29 is inserted into an inner circumferential side in a slot depth direction of a first slot 15a and into an outer circumferential side in a slot depth direction of a second slot 15a three slots away. Then, the free end portions 29c of each of the coil segments 29 extending outwards from the slots 15a at the front end are bent circumferentially outwards away from each other.
Next, as shown in FIG. 9, two winding sub-portions each having one turn are prepared by joining together the free end portions 29c of adjacent coil segments 29. Then, the two winding sub-portions are connected in series to prepare one winding phase group having two turns in which the conductors are wound into a wave winding in every third slot 15a. At that time, at the front end of the stator core 15, the free end portions 29c of the adjacent coil segments 29 are stacked radially and joined, and the conductors of the coil segments 29 are constructed so as to fold back at the joint portions from the inner circumferential side to the outer circumferential side looking from above. Similarly, at the rear end of the stator coil 15, the conductors of the coil segments 29 are constructed so as to fold back at the turn portions 29b from the inner circumferential side to the outer circumferential side.
Two other winding phase groups are prepared in the same manner. The slots 15a into which the coil segments 29 are inserted are offset by one slot in each of the winding phase groups.
The stator winding 16 is constructed by connecting the three winding phase groups constructed in this manner into a three-phase alternating-current connection such as a Y-connection or a xcex94-connection.
In the conventional automotive alternator, the conductors constituting the inclined portions 24b and 25b positioned on the inner circumferential side of the coil ends 24 and 25 constituting the coil end groups 16f and 16r of the stator winding 16 are parallel to each other and inclined at a predetermined angle relative to the axis of the stator core 15. In other words, the conductors constituting the front-end inclined portions 24b on the inner circumferential side are inclined forwards relative to the rotational direction of the fans 5, and the conductors constituting the rear-end inclined portions 25b on the inner circumferential side are inclined backwards relative to the rotational direction of the fans 5.
Thus, at the front end, the cooling air flow discharged from the fans 5 flows smoothly along the inner circumferential surfaces of the front-end inclined portions 25b on the inner circumferential side. At the same time, at the rear end, the cooling air flow discharged from the fans 5 interferes with the inner circumferential surfaces of the rear-end inclined portions 25b on the inner circumferential side, and causes an increase in wind resistance. As a result, the pressure difference between the front end and the rear end is increased by an imbalance in wind resistance between the front end and the rear end, causing the flow QRt of the cooling air flowing through the inside of the rotor 7 to increase. Thus, the overall flow rate of the air drawn in from the front end and the rear end decreases due to the increased loss of pressure inside the rotor caused by the flow QRt. Because a portion of the rear-end intake volume flows into the inside of the rotor, the flow rate of the cooling air flow cooling the rear-end coil end group 16r is reduced, and one problem has been that the rear-end coil end group 16r cannot be cooled sufficiently.
Furthermore, as shown in portion A of FIG. 10, the cooling air flow discharged from the fans 5 has a wind speed distribution in an axial direction. Because the speed of the cooling air flow discharged from the fans 5 is higher at tips of the fan blades 5a close to free edges of the fans 5, the cooling air flow discharged from the fans 5 has a component flowing towards axial edges of the blades.
Thus, because the rear-end inclined portions 25b on the inner circumferential side of the rear-end coil ends 25 located on the blade-facing surface are all inclined backwards relative to the rotational direction of the fans 5, wind noise increases due to interference with the component of the cooling air flow flowing to the axial-edge side, wind resistance increases, lowering the overall air flow rate, and another problem has been that temperature increases in the cooled objects such as the rectifier 12 and the regulator 18 on the intake side of the fans 5 cannot be suppressed.
Furthermore, because the front-end inclined portions 24b on the inner circumferential side of the front-end coil ends 24 located on the blade-facing surface are all inclined forwards relative to the rotational direction of the fans 5, the cooling air flow discharged from the fan 5 flows smoothly along the inner circumferential surfaces of the front-end inclined portions 24b on the inner circumferential side, and yet another problem has been that heat transfer from the front-end coil ends 24 to the cooling air is not promoted, preventing temperature increases in the stator 8 from being suppressed.
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator enabling temperature increases in the stator to be suppressed by matching the inclination of the conductors constituting the inclined portions on the inner circumferential side of the coil ends to the wind speed distribution of the fan, suppressing the difference in pressure between the front end and the rear end to reduce the flow QRt of the cooling air flowing through the inside of the rotor, and ensuring a sufficient flow rate of the cooling air cooling the coil end groups.
Another object of the present invention is to provide an automotive alternator enabling wind resistance to be reduced and enabling the cooling of the internal parts on the intake side to be improved by inclining the conductors positioned on the blade-facing surfaces of the front-end and rear-end coil end groups forwards relative to the rotational direction of the fans 5.
Yet another object of the present invention is to provide an automotive alternator enabling cooling of the stator to be improved by inclining the conductors positioned on the blade-facing surfaces of the front-end and rear-end coil end groups backwards relative to the rotational direction of the fans 5 to promote heat transfer from the coil ends to the cooling air.
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including:
a rotor for forming north-seeking (N) and south-seeking (S) poles about a rotational circumference;
a stator including:
a cylindrical stator core formed in a circumferential direction with a number of slots extending axially, the stator core being disposed radially outside the rotor; and
a stator winding wound into the stator core;
a bracket for supporting the rotor and the stator; and
fans fastened to first and second axial ends of the rotor,
wherein the stator winding includes a number of winding sub-portions in each of which a strand of wire is wound into the stator core in a connection pattern in which the strand of wire is drawn outside first slots, is folded back outside the slots, and enters second slots a predetermined number of slots away to constitute coil ends,
wherein the coil ends are arranged in neat rows in a circumferential direction at a front end and a rear end of the stator core to constitute front-end and rear-end coil end groups, respectively, inner circumferential surfaces of the front-end and rear-end coil end groups constituting blade-facing surfaces, and
wherein portions of the coil ends positioned in the blade-facing surfaces of the front-end and rear-end coil end groups are inclined in an identical direction relative to a rotational direction of the fans.